The present invention relates to blade pitch actuation mechanisms and in particular to actuator supported bearing assemblies for use in propeller blade pitch actuation mechanisms for turboprop engines.
Turboprop engines are well suited to large payload capacity cargo planes due their high propulsive efficiency, i.e. their ability to turn power into usable thrust, which results in high fuel efficiency. Cargo planes typically require multiple engines to produce the power necessary to propel such large, heavily loaded aircraft. Many such multi-engine aircraft utilize opposite rotation turboprop engines, a right-hand (clockwise) rotating engine and a left-hand (counterclockwise) rotating engine on each wing, to reduce the turbulence effect of exit swirl and to reduce torque loads on wing structures.
In a turboprop engine, a turbine is used to drive propeller blades for producing thrust. In a typical configuration, a spool comprising a compressor and a turbine is used to sustain a combustion process and produce hot gas for driving a free turbine. The free turbine, in turn, is used to drive a gearbox that rotates the propeller blades. In order to maintain engine efficiency during flight, turboprop engines are operated at a constant, peak-efficiency speed. Changes in engine power output are controlled by fuel flow and propeller blade pitch, which is controlled by a blade pitch actuation mechanism. Each propeller blade is typically connected to the blade pitch actuation mechanism through a trunnion pin and bearing assembly interface, which provides the force necessary to counter the rotational torque imparted to the propeller blade by the air stream and rotating forces generated by the mass distribution of the blade. The pitch of a propeller blade mounted on a right-hand engine is adjusted in the opposite direction as a blade mounted on a left-hand engine, thus necessitating differences in blade pitch actuation mechanism for left-hand and right-hand engines. It is, nonetheless, desirable to maintain interchangeability of parts for both right-hand and left-hand rotating engines to reduce time and expense in both production and maintenance of the engines. Additionally, the increased twisting moment about the pitch change axis of large propeller blades is translated to the blade pitch actuation mechanism. Thus, the bearing assembly surrounding the trunnion pin, which bears the reactive forces, is typically a high-wear component, especially as the size and thrust output of turboprop engines increase.
There is, therefore, a need to increase the interchangeability of blade pitch actuation mechanisms for left-hand and right-hand configured engines. Additionally, there is a need for a wear-resistant and heavy-duty bearing assembly, as well as for a blade pitch actuation mechanism that permits easy maintenance and assembly.